Magnetic speedometer.



J. K. STEWART.

MAGNETIC SPEEDOMETER.

.APPLIGATION FILED NOV. 5, 1910.

Patented Nov. 4, 191

Wfizessase Um EnsTATEs PATENT OFFICE.

JOHN K. STEWART, OF CHICAGO, ILLINOIS, ASSIGNOB TO STEWART-WARNER BPEEDOMETER CQRPORA'IION, 0F VIRGINIA.

MAGNETIC SPEEDOME' IEB.

Specification of Letters Patent.

Patented Nov. 4, 1913.

Application filed November 5, 1810. Serial No. 580,778.

citizen of the United States, residing at Chicago, in the county of Cook and State of Illmois, have invented new and useful Improvements in Magnetic, Speedometers, of which the following is a specification, reference being had to the accompanying drawings, forming apart thereof.

The purpose of this invention is to provide within a speedometer case means sensitive to temperature changes for automatically regulating the strength of the spring aga-mst which the speed-indicating mechanism is deflected. 4

In the drawings :Figure 1 is an interior plan view of that portion of the speedometer containing the parts embodying the invention, being a section at the line 11 on Fig. 2. Fig. 2 is an axial section of a spec ometer showing the relation of the parts constituting the invention to the other parts of the instrument.

This device is intended for use in the wellknown type of speed-indicating device operated by the principle of magnetic drag.

As illustrated in Fig. 2, 1 is the speedometer case. 2 is the driving shaft, to the upper end of which is secured the magnet-carrier, 3, with its magnets, 4. Adjacent to the magnets and separated therefrom by a slight space is the Inverted cup-shaped element, 5,

journaled concentrically with the rotatable magnets and formed of some non-magnetic metal such as copper or aluminum. The spindle, 6, of this element carries also the indicating needle, 7 in position for traversing the dial lndicated at 8, on Fi 2. A hair spring, 9, having its inner en fastened to t e spindle, 6, and its outer end secured to a part fixed on the case serves to bias the needle toward the zero point, holding it there until the non-magnetic element, 5, carried on the same spindle is deflected by the magnetic drag of the rotating magnets, 4. It is well known that the amount or stren th of this dra depends directly upon the e ectrical con uctivity' of the element, 5, and also upon the velocity of rotation of the magnets, 4. Obviously, a change in either of these determining factors will effect a change in the indication of the needle, 7. It is through the efiect of changes in velocity that the instrument becomes a speed indicator, and the purpose of the present invention is to prevent variations of electrical conductivity from afiecting and vitiating' .crease of temperature causing adecrease in the conductivity of the metallic element, 5.

Since the magnetic drag o crates always in opposition to the strengt of the hair sprmg, 9, it would be suflicient to decrease the stiffness by increasing the operative length of this spring in proportion to the decrease of magnetlc drag occasioned b the decrease of conductivity above recite For accomplishi automatically such variation inthe operative length of the spring, it is mounted within a circular container, 10, concentric with the spindle, 6, having one end secured thereto by means of a rivet or screw,.11. Also concentric with the spindle there is mounted a small radius arm, 12, carrying at its outer end a roller, 13, in position to bear against the outer coil of the air spring and to press it against the inside wall of the container, 10. The other end of the arm is rovided with a small spur gear 14 rigid wlth it. Just within the circular casing, 1, a metallic strip, 15, is coiled preferably close against the casing,- and with the coils touching each other. The outer end of this strip is rigidly secured to the casing, and the inner end is fastened to theshort end, 16, of the segmental lever, 16.

A series of gear teeth is provided on this lever at 16", for meshing with the spur gear, 14. The lever, 16, being fulcrumed upon a stud, 17. nearest the end, 16*, will undergo a considerable angular movement in response to even a slight variation in the length of the coil, 15, due to change of temperature.

As shown, an increase of temperature which would tend to elongate the metallic strip, 15, would move the parts so as to simultaneously elongate the efiective length of the hair spring, 9,.that is, its length between its connection with the spindle, 6, and the bearing point of the roller, 13. This, as above noted, would decrease the resistance of the spring to deflection of the parts by the magnetic drag which .would also have been decreased in effect by the increase of temperature. Thus, when the parts are properly proportioned, changes of temperature, while varying the force upon which the operation of the instrument depends, at the same time automatically correct the action of the parts so that a faithful indication of speed is still furnished by them.

I claim a 1. In a speed indicating device, a scale member, a pointer associated therewith, a spindle connected to one of these parts, a spring having one end connected to said spindle, a split ring device sensitive to variations in atmospheric temperature, and havin one endfixed, connections between the other end of said spring and the free end of said split ring device, and means operated by the shaft, the speed of which is to be indicated, for rotativel moving said spindle against the action'of said spring.

2. In a speed indicating device, a scale member, a pointer associated therewith, a spindle connected to one of these parts, a spring connected to said spindle, a thermostatic device, connections between said thermostatic device and said spring, means operated by the shaft, the speed of which is to be indicated, for creating a rotating magnetic field, and means connected to the spin- I die and acted onby the magnetic field to rotatively displace said spindle against the action of said spring.

3. In a speed indicating device, a magnet and a magnetic mass, a member interposed therebetween to be cut by the lines of force in the magnetic field thereof, a spindle connected to said member, a spring connected at one end to said spindle, a thermostatic device, connections between said thermostatic device and said spring, and means for imparting rotation. to the magnetic mass.

4. In a speed indicating device, means for creating a rotating magnetic field, a member arranged to be rotatively displaced by said rotating magnetic field, a spindle carrying said member, a spring to yieldingly resist the rotative displacement of said member, a thermostatic device and connections between said thermostatic device and said spring to vary the efi'ective tension of said spring by and in accordance with variations in atmospheric temperature.

5. In a speedometer, in combination with a rotating .ma et and a non-magnetic member mounted or oscillation in the magnetic field; a metallic spiral having one end fixed; a spring fixed at one end and operatively connected with said member for biasing the latter to a position of rest; means for hold- I ing the spring fixed at a point intermediate its ends for limiting its effective length, said means comprising a part connected with the free end of the metallic spiral for movement thereby along the spring for a distance from its fixed end.

6. In a speedometer, in combination with a rotating ma et and anon-Ina etic member mounted or oscillation in't e magnetic field; a metallic spiral having one end fixed and means by which it is circumferentially restrained; a spring fixed at one end and operatively connected with said member for biasing the latter to a position of rest; means for holding the spring fixed at a point intermediate its ends for limiting its effective length, said means comprising a part connected with the free end of the metallic spiral for movement thereby along the spring for a distance from its fixed end.

7. n a speedometer, in combination with a rotating magnet and a non-magnetic member mounted for oscillation in a magnetic field; a metallic spiral having one end fixed; a spring having one end operatively connected with said member for biasing the latter to a position of rest; a circular container for the spring, and an element mounted for movement about the axis of such container having means for binding the spring against the latter to limit its efi'ective length, and means connecting said element with the free end of the metallic spiral for movement therewith. I

8. In a speedometer in combination with a rotating magnet and a non-magnetic member mounted for oscillation in a magnetic field; a metallic spiral having one end fixed and means by which it is circumferentially restrained; a spring having one end operatively connected with said member for biasing the latter to a position of rest; a circular container for the spring, and an element mounted for movement about the axis of such container having means for binding the spring against the latter to limit the effective length of the spring, and means connecting said element with the free end of the metallic spiral for movement therewit 9. In a speedometer, in combination with i a rotating ma et and a non-magnetic member mounted or oscillation in the magnetic field; a metallic spiral having one end fixed; a spring having one end 0 eratively connected with said member or biasing the latter to a position of rest; a circular container for the spring; a radius arm pivoted at the center of the container; a roller journaled on the radius arm in position to retain the free end of the spring against the containerv wall, and means connecting the radius arm with the free end of the metallic spiral for movement therewith.

10. In a speedometer, in combination with a rotating ma et and anon-ma etic member mounted Edioscillationv in t e ma etic field; a metallic spiral having one end ed; a spring having one end 0 eratively connected with said member or biasing the latter to a osition of rest a circular container for t e spring; a r usarm pivoted at the'tenter of the container; a roller journaled on the radius arm in position to bind the spring intermediate its ends against the wall of the container; a pinion rigid with the radius arm at its pivotal mounting, and a gear device positioned to mesh with the pinion and connected to the free end of the metallic spiral for movement therewith.

11. In a speedometer, in combination with a rotating ma et and a non-magnetic member mounted or oscillation in the magnetic field; a metallic spiral having one end fixed; a spring having one end operatively connected with said member for biasing the latter to a position of rest; a circular container for the spring; a radius arm pivoted at the center of the container; a roller journaled on the radius arm in position to bind the spring intermediate its ends against the wall of the container; a pinion rigid with the radius arm at its pivotal mounting; a gear segment journaled in position to mesh with the pinion, and means connecting said gear segment to the free end of the metallic spiral for movement therewith.

12. In a speedometer, in combination with a rotating magnet and a non-magnetic member mounted for oscillation in the magnetic field; a metallic spiral having one end fixed; a spring having one end operatively connected with said member for biasing the latter to a position of rest; a circular container for the spring; a radius arm pivoted at the center of the container; a roller journaled on the radius arm in position to bind the spring intermediate its ends against the wall of the container; a pinion rigid with the radius arm at its pivotal mounting, and a lei'er fulcrumed between its ends and having a gear segment formed on one end in position to mesh with the pinion, the free end of the metallic spiral being connected to the other end of the lever for moving it.

In testimony whereof, I have hereunto set my hand in the presence of two witnesses, at Chicago, Illinois, this 29th day of October 1910.

v JOHN K. STEWART. \Vitnesses:

- G. L. MEYER, Jr.,

STANHOPE Hunson. 

